The real books · Page 5 of 5
Bowditch: finding your way around
The American Practical Navigator, first published by Nathaniel Bowditch in 1802, is the United States’ reference book of navigation. NGA keeps it up to date and gives it away as a PDF. It is a book to look things up in, not a course: read the chapter on a topic after you have learned it, and it fills in the why, the history and the special cases.
The two volumes
- Volume I is the text, in ten parts. Part 3, Celestial Navigation (chapters 14 to 20), is the one for this course. Part 2, Piloting, holds compasses, dead reckoning and the sailings.
- Volume II holds the useful tables (among them amplitudes, distance of the horizon, time zones, and natural trigonometric functions), the calculations behind them, appendices (among them the navigational stars and planets, and extracts from a real Nautical Almanac), and a glossary of navigation terms.
Where the course is in Bowditch
| In this course | In Bowditch (2024 edition) |
|---|---|
| Latitude and the nautical mile | Vol. I, ch. 10 Dead Reckoning; ch. 13 The Sailings (course and distance, including great circles, which this course does not cover) |
| Angles, time and UT | Vol. I, ch. 17 Time; Vol. II, ch. 3 Time Measurements and Conversions, and Table 26 Time Zones, Zone Descriptions, and Suffixes |
| Where the Sun is: GHA and declination, The circle of equal altitude, The assumed position and LHA | Vol. I, ch. 14 Navigational Astronomy (the celestial sphere, hour angles, the navigational triangle); ch. 18 The Almanacs |
| Sextant corrections: Hs to Ho | Vol. I, ch. 15 Instruments for Celestial Navigation; ch. 16 Sextant Altitude Corrections; Vol. II, ch. 6 Sextant Altitude Corrections |
| Latitude from the noon Sun, Latitude from Polaris | Vol. I, ch. 20 Sight Reduction (latitude by meridian altitude, and by Polaris) |
| The line of position, The intercept method | Vol. I, ch. 20 Sight Reduction; Vol. II, ch. 7 Calculations of Celestial Navigation and ch. 8 Sight Reduction (the formulas behind the tables) |
| Planning a twilight fix | Vol. I, ch. 19 Sight Planning |
| The fix | Vol. I, ch. 20 Sight Reduction (plotting the fix); ch. 3 Navigational Errors (judging it) |
| Planets and the Moon | Vol. I, ch. 14 and ch. 18; Vol. II, Appendix A Navigational Stars and the Planets |
| Checking the compass by the Sun | Vol. I, ch. 9 Compasses; Vol. II, ch. 4 Compass Error, and Table 22 Amplitudes |
Using it well
- Search the PDF for a term (say “dip” or “Polaris”) rather than leafing through 800 pages.
- The glossary at the end of Volume II defines every term you will meet.
- The almanac extracts in Volume II are real Nautical Almanac pages: once you have finished the course, work a sight from them on paper, with the printable sight form, to see that the books and the course agree.
- Chapter 29, Emergency Navigation, is worth a read: what to do when the electronics, or the almanac, are gone.